() => {
    //函数类型声明方式1: 单独制定函数和返回值的类型
    function fn1(a: number, b: string): string {
        return "1"
    }


    const fn2 = (a: string, b: string): number => {
        return 1
    }

    //函数类型声明方式2: 同时指定参数 返回值的类型
    type fn3Type = (a: number, b: string) => string

    const fn3: fn3Type = (a, b) => {
        return "1"
    }

    const fn4: (a: number, b: number) => number = (a, b) => {
        return 1
    }
}